CHEMISTRY OF S/GAAS AND METAL S/GAAS SYSTEMS

Bonding states and the band bending of S/n-GaAs (001) and metal/S/n-GaAs (001) systems are studied by synchrotron radiation photoemission spectroscopy (SRPES). The difference in the surface chemistry between the (NH4)2Sx-treated GaAs and the sulfur-chemisorbed GaAs is explained well by the formation of the sulfur-rich transition layer for the (NH4)2Sx-treated GaAs. A structural model for the annealed S/GaAs (001) system is proposed, in which the surface is terminated with Ga-S bonds. The barrier height of the Al, Au, and In Schottky contacts on (NH4)2Sx-treated n-GaAs is also determined to be about 0.4, 0.7, and 0.3 eV, respectively, by SRPES for the first time, which are in fairly good agreement with I-V characteristics of the metal/S/n-GaAs Schottky diodes. It is found that the oxide-free interface with a sulfur interlayer plays an important role for the metal-dependent Schottky barrier formation.